I've still not seen consensus on whether these springs ever wear out - many contend they never do. So unless one of yours is clearly broken somehow, I suggest looking into some other possible culprits first, like the pads that are on top of the shocks, or you might even check the rear of the car, how the suspension is looking there: also here there are pads, donuts at the trailing arms, etc. (because I recall Jim Villers telling us that his front was too high not because there was anything wrong with the front suspension but, rather, because his rear suspension was sitting too low).
But if I were replacing a spring because it was broken, I would go for all four, just to get it done and over with. If you go that route, I would suggest carefully matching the new ones to the old ones, or else you could be battling another ride height issue for a while.
Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic